Rate-Topics can be used to DoS individual (public) topics

[binwiederhier]

The attack is this:

• Subscribe to mytopic with the rate topics header including "mytopic"
• Everyone who subscribes to that topic will count towards that one IPs 250 message limit
• After 250 messages, done

I will remove the rate-topics header entirely as a result, and just enable visitor rate limiting for "up*" topics.

[binwiederhier]

#1049